The present invention has a number of application areas. One important application is for transport or storage of volatile and flammable fluids in large tanks such as ship tanks in connection with transport of different types of hydrocarbon containing liquids.
In tanks of the type mentioned vapour and gas of the most volatile components of the liquid, which are also the most flammable components and furthermore toxic, will rapidly form. These gases and vapours will establish equilibrium with the corresponding components in the liquid phase under formation of a certain overpressure in the tank. Generally these types of components are denoted “volatile organic components”, VOC. Motion and varying temperature conditions can influence on this process in the direction of a higher pressure. In addition to the economic loss the formed gas represents a safety hazard.
The safety problem is mainly related to oil transport on tank ships. Evaporation of gas from the liquid leads to an increased pressure in the tanks and thus a need for pressure reduction to ensure that the tanks are not damaged. This has commonly been achieved by manually opening a valve which is typically localized mid-ships. Under tough weather conditions this is in itself a safety hazard. There is also a safety risk related to the possibility of too low pressure which may lead to undesired introduction of air into the tanks and a resulting formation of explosive gases therein.
The economic loss is related to the evaporation of components from the liquid, e.g. oil, so that the ship arrives at its destination with less liquid than was loaded.
Many attempts have been made to overcome these problems in different ways that generally can be divided into two categories. The two categories or systems both involve absorption of gas in the liquid for which it has evaporated. First category comprises systems that are arranged on the deck of the tank and is exemplified by Norwegian patent No. 316 045, U.S. Pat. No. 6,786,063 and U.S. Pat. No. 3,003,325. The second category comprises systems that are embedded within the tanks and is exemplified by Norwegian patent No 315 293 and Norwegian patent No. 315 417.
Disadvantages with the known systems are partly that they are less effective than desirable and also they do not avoid all safety risks or other disadvantages.